What is the Large Hadron Collider?
Journey inside the LHC, the largest and most powerful particle accelerator ever built.
The LHC is the largest and most powerful particle accelerator ever built. It took international teams numbering in the thousands to design, construct and operate the 27 km collider and its four giant particle detectors and was designed and built on the back of decades’ worth of expertise, technology and machinery – both from CERN’s own past and from the wider international physics community. A decade in the construction, the LHC stands as a monument to human ingenuity and ambition.
What is a collider?
In some ways, a collider is a simple and rather brutal device. They take tiny particles, accelerate them to tremendous speeds, and smash them into each other. The reason is not to break particles apart to see what they are made of, but to create altogether new particles from the energy of the collisions.
In this sense colliders aren’t 'atom-smashers', but particle factories, creating new and exotic matter from pure energy. By studying these new particles, physicists learn more about the physical laws that govern our universe at the most fundamental level.
Colliders vary in design. Some, like enormous rifles, fire particles at each other in straight lines, while others whirl them round a ring. The type of particle selected for colliding also differs, ranging from everyday electrons to more exotic particles of antimatter.
CERN’s Large Hadron Collider (LHC) is the largest and most powerful particle collider ever built. Housed in a 27-km tunnel beneath the Swiss-French border, it fires two beams of hadrons around and around in a circle before colliding them into each other. A hadron is a category of particle, and includes the stuff that makes up the atomic nucleus: neutrons and protons. The LHC mostly uses protons, but occasionally picks much larger projectiles, such as lead nuclei.
Along one of the LHC’s straights, sit sixteen radio-frequency cavities that each give the beams a 2-million-volt energy boost every time they pass (a whopping 11,000 times a second).
Eventually, the protons reach 4-trillion electron-volts, travelling at 99.999997% the speed of light. At that speed, persuading the protons to go in a circle, even around a curve as gentle as the 27 km LHC ring, requires applying an absolutely enormous force.
Steering and focusing
Most of the LHC ring is made up of magnets, which have the formidable task of controlling the highly-energetic particle beams. All the magnets are superconducting, a miraculous property which means they offer no electrical resistance, allowing the generation of tremendously powerful magnetic fields. The magnets only superconduct at extremely low temperatures, and must be cooled using liquid helium to -271.25°C – colder than deep space, and two degrees above the lowest temperature possible, absolute zero.
The LHC was designed and built on the back of decades’ worth of expertise, technology and machinery – both from CERN’s own past and from the wider international physics community. A decade in the construction, the LHC stands as a monument to human ingenuity and ambition.
Written for the Science Museum's Collider exhibition, 2013. © Creative Commons - CC BY